1. Field of the Invention
This invention relates to drilling drain holes in the earth. More specifically, apparatus and method are provided for creating a hole in a well casing using a rotary mechanical or nozzle cutter operating through a tool body and then aligning a guide channel in the tool body with the hole in the casing for jet drilling of a lateral drainhole with a jet bit on a flexible tube.
2. Description of Related Art
There has been increasing interest in jet drilling of drainholes around oil or gas wells to enhance the production and injection rate of wells. Proposed methods generally include drilling a hole in the casing of a well and then drilling a drainhole through the hole in the casing. U.S. Pat. No. 5,853,056 discloses placing a tubing in casing with an “elbow” (diverter) at the bottom, inserting a flexible shaft with a ball cutter attached, making a hole through casing with the ball cutter, removing the ball cutter from the well and, without moving the tubing, inserting a flexible hose through the hole to jet drill a drainhole. The tubing may be turned to drill a drainhole in another direction using the same procedure, requiring running the tubing in and out of the well for the ball cutter and for the jet drill. U.S. Pat. No. 6,263,984 discloses placing a diverter attached to tubing in a well, placing a jet bit on flexible tubing, placing the jet bit through the diverter, jet drilling through casing and continuing to jet drill a drainhole into a formation. U.S. Pat. No. 6,668,948 discloses a nozzle for jet drilling. U.S. Pat. No. 6,283,230 discloses a rotating fluid discharge nozzle passing through a diverter and drilling through casing and into a formation. U.S. Pat. No. 7,168,491 discloses a tool for aligning fluid nozzles for drilling holes in the casing or flexible hoses for drilling drainholes by using a spring-loaded plunger that enters an existing perforation and allows alignment for drilling additional holes in the casing or drainholes into a formation.
For a formation at a depth of 5,000 feet, for example, each travel up and down the well with the apparatus on tubing requires about two hours, assuming there are no difficulties. If the apparatus must be removed from the well for each hole in casing and each drainhole, a minimum of about four hours travel or operating time is required for each lateral (drainhole). For six laterals to be jet drilled at the same level in a well, twenty-four hours operating time is required just for the apparatus to be moved up and down the wellbore. Apparatus and method are needed to allow reliable entry of a jet bit into holes in casing, leading to a decrease in the required operating time to drill multiple laterals at the same depth or elevation in a wellbore.